( cliii ) 



them are united to form a knob. In the Platypsyllidae and 

 SipJionaptera the antennae recall those of Clavicorn beetles 

 (text-figs. 14-19, 21). 



The incisions between the segments of the body and leg- 

 joints are points of danger; the hairs of the host might slip 

 into the sutures and the parasites thus become entangled. 

 This danger is overcome on the one hand by the presence of 

 bristles which overbridge the incisions, and on the other by 

 the segments being closely applied to one another or tele- 

 scoped. Such " parrying " bristles fending off the hairs of 

 the host are most conspicuous at those joints where the 

 greatest flexibility obtains between parts of the insects ; for 

 instance, at the joint between head and thorax, prothorax 

 and mesothorax in those cases where the former is separated, 

 and at the juncture of femur and tibia. Some species of 

 fleas and Polyctenidae may be mentioned as illustrations. 



The bristles which lie flat on the body, as do the majority 

 of the thoracic and abdominal bristles in fleas, not only 



22 X. 



23 



Fig. 22. Abdominal bristles of Xipliiopsylla hippia Roths. (1913). 

 ii 23. „ ,, ,, Polyplax enormia K. and P. (1915). 



